Fire alarm system and repeater



- 9, 1932. v, DURBm 1,870,988

FIRE ALARM SYSTEM AND REPEATER 4 Sheets-Sheet 1 Filed March 21. 1929 mmsa V. DURBIN Aug: 9, EQSZ.

FIRE ALARM SYSTEM ANDREPEATER Filed March 21, 1929 4 Sheets-Sheet 2 .5?- K waacmm Aug. 9, 1932.

v. DURBIN 1,870,988

FIRE ALARM SYSTEM AND REPEATER Filed March 21. 1929 4 Sheets-Sheet 3 Aug, Q, 1932.

v. DuRBm 1,87,98

FIRE ALARM SYSTEM AND BEPEATER Filed March 21, 1929 4 Sheets-Sheet 4 4%W8f? fi z 4 Var/La I M wire sr'rss P'rn- VERNON DURBIN, OF NEWTON, MASSACHUSETTS, ASSIGNOR TO I'IOLTZER-GABOT ELEG- TRIC COMPANY, OF ROXBURY, MASSACHUSETTS, A CORBORATIONIOF MASSACHU- SETTS Application filed March 21,

vide for non-interference and succession as between boxes which are pulled to gain simultaneous control of the system.

Another object is to provide protective devices, which upon occurrence of a fault will ive appropriate signals, whichwill maintam in operation all parts of the system except those directly connected with the faulty part, and which will automatically restore the entire system to normal condition upon 29 repair of the fault.

A still further object of the invention is to devise an electrical repeater, which is of simple and reliable construction, and which operates to effect the above ends in the systerm.

With these and other objects in view as will hereinafterrappear, the present invention consists of the fire alarm system and repeaterhereinafter described and particularly' defined in the claims.

In the accompanying drawings illustrat ing the preferred form of the invention, Fig. 1 is a diagram of the preferred form of fire alarm system employing two box cir-. cuits; Fig. 2 is a plan view of the preferred form of repeater; Fig. 3 is a side elevation of the repeater; Fig. 4: is a detail view showing the positions of the repeater armatures when the non-interference magnet is (lo-energized; Fig. 5 is a view of the repeater showing the positions of the parts when a box circuit is open Fig. 6 is a detail view of the repeater when the detent armis released; Fig.7 is a diagram of the-repeaterland associated circuits when one box circuit is open; Fig. 8 is a diagram showing the blocking effect of the armatures; and Fig. 9 is a diagram of a suitable form-of box for use in the system. 7 i

The illustrated embodiment of the inven- FIRE ALARM SYSTEM AND BEPEATER 1929. Serial No. 348,895.

plurality of box circuits each of which in-z cludes a series of separate boxes. The sev eral box circuits are interconnected. by

means of non-interference repeaters. j The repeaters are constructed and'arranged to prevent interference between boxes in different circuits to'thesameextent that interference between boxes in the same circuit is prevented by the construction of the boxes themselves. Moreover, the system as a whole is successive 'tothe same extent that the boxes in any single circuit are successive. In the final analysis, therefore, the system as a whole has the same degre'eof non-interference and succession as exists be tween boxes in any box circuit.

Referring to the drawings, the systemco-mprises a plurality of box circuits indicated as two circuits B and B each including a plurality of boxes 10, a battery 12, a currentlimiting resistance 14, and anautomatic register 16.. Each box circuit is a normally closed circuit. The boxes are of any suitable construction but are preferably of a non-interfering and successive type. Such types of boxes are old and well-knownin the art, but for the sake ofcompleteness a specific description'of-one form thereof is appended at the end of the specification. It is sufficient to say at this tme that thepreferred box, in

common with other boxes of similar construction, operates to send in a signal by opening and closing of the box circuit by means of acode wheeheaoh box being provided with mechanism whereby it is rendered inoperative if when it is itself closed, it looks into an open line. If a box is pulled, therefore, while the circuit is open for any reason, as by the sending inof a signal by another box it will be temporarily rendered ineffective to send in a signal, but after a predetermined number of rotations of its code wheel, usually either one or four rotations,-it again looks into or feels of the line, and if it then finds the line closed, itmaythen send inits own;

signal. This construction of the boxes affords complete non-interference and successionas betweeen boxes in-the same circuit. According to the present 1nvent1'on,itherepeater sys-- tem gives the same degree of non-interference and succession between boxes of difi'erent box circuits as exists .between boxes in the same circuit.

At the central station, each box circuit terminates in a repeater, indicated respectively for the two circuits at R and R the construction of which is shown in Figs. 2 and 3. Each repeater consists of two interlocking relays, namely, a box circuit relay and a non-interference relay indicated gen-- erally at 20 and 22 respectively. The box circuit relay consists of an electro-magnet 24 which is in series with the-box circuit and which normally attracts an armature 26. Secured to the armature are supporting arms 27 and 28 and a contact arm 29, all mounted on a shaft 3-0 which is pivoted in adjustable bearings 32 in standards 33. The contact arm 29 carries contact springs 34 adapted to engage adjustable contact 7 screws 36 mounted on a lever 38 which is loosely pivoted on the shaft 30 and insulated therefrom. The lever 38 has provision for a limited movement permitted by a notched detent arm 42 which will subsequently be described in detail. In Fig. 1, the contact levers 29 and 38 with their contacts 34 and 36 are diagrammatically illustrated. The non-interference relay. 22 comprises an electro-magnet 44 having an armature 46 mounted on the pivoted rod 47 which is provided with spring contact members 48 adapted to engage fixed contacts 50. The contacts 48 and 50'are in the box circuit and are normally maintained closed by the attraction of the magnet 44 so that when the box circuit is closed, the box circuit relay magnet 24 will be continuously energized. The magnet 44 attracts its armature against the pull of a spring 51. V

A feature of importance to which reference will be made later consists in means for interlocking the armatures of the non-interference and box circuit relays so that when one of I the armatures is permitted to move to open position by de-energization of its corresponding magnet, it looks the'other armature in closed position. As shown in Fig. 3, the armatures are normally maintained by their magnets in such positions that, their contacts are held closed. The box circuit relay armature 26 is horizontal, and the non-interference relay armature 46 is vertical. The supporting lever 28 of the horizontal armature 26 is extended to form a locking lever, 52 which is normally urged downwardly against the attract-ionof the magnet by a spring 54. As shown in Fig. 3, the lever 52 has a shoulder 56, and at the extreme end it is provided with a hook shaped projection 58. The noninterference relay armature 46 carries a blocking lever 59 which is formed nearits endwith a shoulder 60. The shoulder 56 on the lever 52 isadapted to form an abutment for the end of the lever 59 when the non-interference relay is de-energized and the shoulder 60 forms an abutment for the lever 52 when the box circuit relay is deener'gized. The levers 52 and 59 which are associated respectively with the box circuit relay armature and the non-interference relay armature constitute interlocking means by which the release of one of the armatures blocks movement of the other.

repeater R and thence through the wire 76 to the line L. Thus the contacts 34 and 36 of all of the repeaters are connected in series with the battery and the non-interference lines. The windings of the magnets 44 of the non-interference relays are connected by wires 80 across the lines L and L. A station signal relay S is also connected across the lines and controls an armature 81 included in a normally closed station signal circuit, which circuit comprises a battery 82, audible alarms 84, and a register 86. It will be seen, therefore, that if the contacts 34 and 36 of any box circuit relay are opened for any reason, the repeater circuit is opened and all of the non-interference magnets 44, as well as the station signal relay S, are de-energized. Such a result is produced by the openin of a box circuit, whichis usually occasioned by the starting of a box to'send in a signal.

' It will be seen that the box circuit relay arma-tures control the non-interference cir-" cuit, and the non-interference relay armatures control the opening and closing of their respective box circuits.

Whenever a box circuit is opened for any cause, its box circuit relay is tie-energized and its lower contact arm 29 is permitted to fall into the position shown in Fig. 5, thus opening its contacts 34 and 36 and de-energizing the non-interference lines. The contact lever 38 also falls slightly, being stopped by the notch of the detent arm 42. The non-interference relays of, all' other repeaters are therefore de-energized. to permit their armatures to fall under the box circuit relay armatures, thereby holding the latter in closed position, as shown in Fig. 4. In this figure,

the armature 26 has been permitted to retract slightly by the de-energization of its magnet but by the blocking effect of the noninterference relay lever 59, the retraction is not suflicient to open the contacts 34 and 36. This condition is diagrammatically illustrated in Fig. 7 ,wherein it is assumed that circuit- B through the repeaters.

the circuit Bhas opened, thereby opening the This opening of circuit B is the means bywhich all of its boxes are rendered inoperative, because if abox in circuit B is then pulled, it is in the condition of being closed while looking into an open line. N hen the circuit B is again closed, the armature 26 is again attracted, thereby closing the non-interference circuit and restoring the parts to original position. The attraction of the armature 26 in circuit B unblocks the armature-.46 but this unblocking action is retardedfora time su'liicient topermit the current to build up in the non-interference circuit. It will be seen that inasmuch as the lever 38 of the repeater is permitted some slight pivotal movement when the armature 26 is released, the contacts 34 and 36 will close before the end of the lever 52 rises sufiiciently to unblock the armature 46. This condition is shown diagrammatically in Fig. 8 wherein the contacts have just been made but the armature 46 still remains blocked by the horizontal lever. The pivoted lever 38 is provided at its end with a wei ht 88 which materially retards the attraction movement of the armature 26 after the contacts have been made. This retarded movement afi'ords sufficient time for current to build up in the inductive non-interference circuit before the non-interference relay armature is mechanically released. Moreover, the local circuit ofeach non-interference magnet is designed with a small time constant. This result s accomplished by including in the circuit 80 a resistance which is in series with the non-interference magnet. The time constant of a circuit is the ratio of inductance to resistance and is the time in which the current builds up approximately to 37% of its permanent value. The smaller the time constant, the more'rapidly will the current build up in the inductive circuit. The use of the series resistance reduces the time constant sufiicientlyso that the current will build up to the proper value to hold the armature 46 in the time interval'during which the armature remains blocked by the lever 52. If this provision for building upthe current were not provided, there would be an interval in which the armature 46 would be neither under the mechanical control of the box Circuit relay armature nor the magneti'c control of the non-interference magnet, so that it might therefore fall away from the magnet to open the circuit at an improper time.

By means of the hook 58, unblocking of the box circuit relay armature of the circuit B is temporarily prevented when the circuit B is again closed. The armature 46 ofthe repeater R having dropped under the lever 52 has blocked the latter armature and has also opened. thebox circuitB at the contacts 48 and 50. "As soon as the non-interfer ence magnet of repeater R isenergized by the closing of circuitB, the armature 46 is attracted. The attraction of the armature 46 closes the circuit B and thereby energizes the box circuit relay 24. -However, the attraction of the relay 24 for its armature 26 isnot' immediate because of the time lag in the building up of the box circuit current, and accordingly, if the lever 52 were immediately unblocked, it would be permitted to fall, thereby again opening the non-interference circuit. The hook 58 on the end of the lever 52 prevents such action. \Vhen the armature 46 is.attracted,.the contacts 48 and 50 are immediately closed, but the armature is restrained from returning to its normal position by the hook '58. This hook holds the lever 59 under the lever 52, thereby blocking the latter against falling until the current in the relay 24builds up sufliciently to at tract. the armature 26. This attractioniof the armature 26 then lifts-the hook sufliciently to let the armature 46 pass. It will therefore be seen that the armatures of both relays of all the repeaters are held under positive interlocking control at all times, either magnetically by their corresponding relays or mechanically by the interlocking.

effect of the armatures.

Although either armature is held temporarily blocked after attraction of the other, a featureof importance consists in thecons'truction whereby the unblocking of the noninterference relay armature is merely re tarded until the inertia contact a'rm'of the box circuit relay is raised, whileunblocking of the box circuit relay armature is actually prevented'by the hook 58 until the box circuit current builds up sufficiently to lift the hook. This distinction is important in the operation of the repeaters to prevent interference between two or more boxes pulled simultaneously, as will hereinafter'appear.

The system thus far described is completely operative for all conditionsof signaling Provision is also made for pr-otec tion of system in case of breaks or open cir-. cuits, but before proceeding to a description of such protective apparatus, the operation of the system for normal signaling will first be explained. Assume that a box in circuit B is pulled. As soon as the code lever of r the box drops into a toothoif the code'wheel, the box circuit is opened. The boxcircuit relay 24 is dis-energized, thereby letting fall the lever to block the armature 46,-as shown 1n Fig. '5. .Also the non-interference lines are de energized, and the non-interference armature 46 .of the repeater R jfalls away from its magnet, opening the circuit B andblocking the horizontal armature (Fig. 4). The circuit arrangements for both box circuits are diagrammatically shown in Fig. 7 YVhen circuit B is again closed bythe code lever of the box, the relay magnet 24 is again energized and as describedabove,

. the repeaters in all of the circuits are restored 5 by the box in circuit B,

to their original positions. The cycles of operations are repeated for each opening and closing of the box until the signal is completed. If during the sending of a signal a box in circuit B is pulled, it will be seen that the second box, before its code lever can drop into a tooth of the code wheel, will look into an open line. Because of the construction of the boxes, the box is rendered inoperative for a predetermined number of rounds, usually either one round or four rounds, after which time it again tests the line and if it finds the line closed, it will then be rendered operative to send in its own signal. If the construction of the boxes is such that the line is tested at the end of each round, it may occur that a box in circuit B will transmit one or more rounds, a box in B one or more rounds, and then the first box may take up the signal again. However, each round is a clear signal and there is no possibility of jumbling.

- Upon each opening of a box circuit, the box circuit signals 16 are operated. Also upon each opening of then-on-interference lines, the station relay S which is connected across the line, is de-energized,-thereby operating the station signals 84 and 86. These signals are of the normal closed circuit type which operate only upon opening of the circuit. N o matter what box is signaling, all of the signals operate in unison.

As explained above, the system is truly non-interfering and successive when noninterfering and succession boxes are employed to the extent that no jumbling of sig-' nals is permitted in the event that one box is pulled while another is signaling. The sys- V tem is equally non-interfering and successive in the event that two boxes in different circuits should open to gain control of their circuits atexactly the same instant. In such a case, assuming that the circuits B and B are opened by boxes in the separate circuits at the same instant, then both repeaters R and R assume the position shown in Fig. 5. If the system comprises more than two box circuits, all other repeaters will operate to open their box circuits in the usual manner. As soon as the code wheels of the two pulled boxes have advanced suiiiciently, they tend to close their box circuits, and althoughit is possible that they might continue 1n synchronism up to the point of closing, the probabllityis that one of the box circuits Wlll be closed by its box slightly in advance of the other. 'Assuming that circuit B closes ahead of B circuit B will then be locked out from further participation in the signahng until such time as the locked-out box again tests the line. This locking-out action is as follows: When circuit B closes,'the armature 26 of repeater R is attracted. The armature 46 of the non-interference magnet,

' however, is not now maintained under positive electrical and mechanical control because when the armature 46 is unblocked by the lever. 52, the magnet 44 still is de-energized because box circuit B has not yet closed. Therefore, the armature 46 falls away from the magnet 44, again opening circuit B. As soon as circuit B is closed, however, the noninterference magnets 44 of both repeaters are energized and the armature 46 of repeater R which was permitted to fall away momentarily is again attracted, and box circuit B is again closed. This momentary opening of the circuit Bis the means for locking the box out of operation, that is to say, the box while in closed condition has momentarily looked into an open line andis therefore prevented from participating in any signaling until it again tests the line. It will be seen that the momentary opening of the circuit B by the falling away of the armature 46 will give an extra tap on the register 16. This extra tap will not appear on any of the other signals of the system; in fact, even as recorded on the box circuit register, it cannot be mistaken for a regular tap. Except for this extra tap on one register, all signaling devices operate exactly as if the box in circuit B had never been pulled. The occurrence of this extra blow therefore indicates that two boxes have been started in unison and that a subsequent call may be expected from the box in circuit B after that in circuit B has completed its signal.

Still assuming that two boxes in different olrcuits gain control of the system simultaneously, it is conceivable that the boxes may open their circuits together and then close them together but'that on the next opening, the box in circuit B will open before that in circuit B. In such a case, the box in circuit B gains control, the action being'no different from the action which occurs when a box is locked out if it endeavors to break in at any time during the signaling by another box. It will be noted that in this event, the extra tap in the circuit of the locked out box is not given. 7

Therefore, if two boxes are started in unison, provision is made fortransmitting clear signals all over the system by one box only,

after which the other box may transmit its own signal, provided the boxes are of the succession type. N o matter how closely the boxes work in synchronism, a time must eventually come when one box will either open or close its box circuit ahead of the other box. The box in the circuit which is held open while the other is closed is the one which gains immediate control. So long as the boxes work together, they signal in unison, but when they fall out of synchronism, one of them is thrown entirely out of operation. Of course, after a predetermined number of rounds, the locked-out box, if it is of the succession type, will test the line, and if it finds it closed, it will then send in its own signal.

T he operation of the system for all possible conditions of signaling having been described, it remains to consider the protective circuits whereby the system' is protected against a break or open circuit. The fault which is most likely to occur is an open circuit in one of the box circuits. According to the invention, provision is made for actuating a. time relay upon each opening of a box circuit, the relay operating after a predetermined interval, longer than any interval required in normal signaling, to cut the faulty circuit out of commission while permitting the remaining box circuits to stand in readiness, as usual, for proper signaling. Associated with each repeater is a tripping relay 91 which when energized attracts an armature 92 on the detent lever 42. The detent lever is normally held in the position of Fig. 3 by a spring 94. The tripping relays are all connected in series in a tripping circuit which leads from the Wire 72 through a current limiting resistance 96, all of the relays 91 in series, a supervising relay 98, and the line L to the negative side of the battery. The supervising relay 98 is of sufficiently high resistance to limit the current in the tripping circuit to such a value that the detent armatures 92 are not attracted. VVhen the relay 98 is short circuited, however, the tripping circuit current rises to a suflieiently high value to attract all of the armatures 92 of the several repeaters, thereby moving each detent arm 42 out of engagement with the lever 38. This energization of the tripping circuit is arranged to occur only upon the occurrence of an open circuit of excessive duration in one oi the box circuits. In order to energize the tripping circuit, a time relay WhlCll'lS indicated generally at 100 is employed. The time relay may be of any suitable construction acting to short circuit the supervising relay after one of the. box circuits has been opened longer thana predetermined time. It is preferred to employ the relay of the type disclosed in the copending application of Durbin, Serial No. 848,896 filed of even date herewith. Suiiice it to say here that the time relay comprises an electro-magn-et 102 connected by wires 104 and 106-directly across the non-interference lines. The magnet normally attracts an armature 108 which under normal conditions is adapted through suitable connections to maintain a contact arm 110 out of engagement with a fixed contact 112. Upon de-energization of the magnet 102, the arm 108 rises and the contact lever 110 is permitted to fall. The time which is required for the arm 110 to move from its normal elevated position to its contact making position may be about 85 seconds, which is longer than the longest interval which a box is required to hold any box circuit open under normal signalling conditions. If a circuit is opened for a time longer than this predetermined period, the magnet 102 is deenergized for a suflicient time to let the con- I tact be made between the lever 110 and the fixed contact 112. The lever 110 is electrically connected to the Wire 104 which as will be seen from Fig. 1 is connected to the line L at one side of the supervising relay 98 while the contact 112 is connected to the other side of the relay. The closing of the contacts therefore short circuits the supervising relay Which permits the current to build up in the tripping circuit sufliciently to attract the detent lever 42.

Under ordinary signalling conditions, the non-interference lines and the time relay magnet are de-energized and re-energized in synchronism with the opening and closing of the active box circuit. The time relay armature 108 is released at each opening, but is immediately attracted as soon as the box circuit is again closed, the open interval being too short to permit closing on the contact 112. Now assume that box circuit B has an open circuit of greater duration than 35 seconds. On the first opening of the circuit, repeater R assumes the position of Fig. 5 and R the position of Fig. 4. After the predetermined time has elapsed, the time relay closes, short circuiting the supervising relay, so that the tripping circuit is energized and the detent arms are attracted.

The repeater R in the open box circuit then has its lever 38 released, and the lever drops into the position shown in Fig. 6, again closing the contacts 34 and 36 which close the non-interference lines. All other repeaters, which at the time of the break assumed the position of Fig. 4, are restored to normal. The closing of the non-interference lines again energizes the time relay magnet 102, thus breaking the contacts 110 and 112. The whole system is therefore restored to normal condition with the exception of the box circuit in which the break occurred, the repeater R in that circuit still holding the position of Fig. 6 with the exception that the detent arm 42 has been released by its magnet 91 and lies against the tail of the lever 38. When the break is repaired, the box circuit B is closed, the repeater magnet 24 is energized, and the armature 26 is attracted to its initial position. Restoration of the circuit to normal after repair of the break is therefore entirely automatic. Y

The short circuiting of the supervising relay 98 is employed to give a signal; The relay normally attracts an armature 114 Which upon de-energization of the magnet is permitted to close a circuit on a contact 116. The circuit is a normally open signal circuit in cluding a bell 118 and a lamp 120. An open box circuit therefore gives two signals, first a general signal on-all of the devices of the terlocked.

system occasioned by the opening of the circuit, and second, a signal in the supervising signal apparatus occurring after the lapse of the predetermined time interval for which the relay 100 is adjusted.

The time relay will also act to operate the supervising circuit in the event of an open circuit in any of the wires 72, 7 4 and 76, as well as the line L.

If a special signal is not desired on the operation of the time relay, an ordinary resistance may be substituted for the supervising relay, this resistance being sufficientto normally limit the tripping circuit to value ineffective to actuate the detent arms.

In the event of a break in one of the noninterference magnets 44 or the wires connecting it with the non-interference lines, that particular magnet 44 is of course de-energized, permitting its armature 46 to fall away and open its box circuit. This gives a single tap on its register 16 but affects no other box circuit or signal in the system.. In case of a break in the line L", one ormore signals will be given, depending on the position of the open circuit. Thus, an open circuit at- :12, between the station signal relay S and the first repeater, will sound a single blow on the station signals, but none of the box circuits or repeaters will be affected. A break at 3 beyond the first repeater will de-energize the magnet 44 of repeater R as well as the relay S, permitting a signal to be given on the station signals as well as on the box circuit signal 16 of circuit B circuit B will remain open but subsequent box circuits will be unaffected because the complete circuit can be traced from the battery through their relays 44. H

Although various types of non-interfering and succession boxes are well known, a description of a suitableform of box is given below for the sake of completeness. The box is diagrammatically shown in Fig. 9. The box comprises a code wheel 130 having the usual initial stopping land 132 and code teeth 134. A code lever 136 cooperates with the code wheel and actuates spring contact levers 138 and 140. One side of the box circuit B connectsv with the contact 138 and the other side of the circuit connects through the electro-magnet 142 with the contact 140. A short circuiting lever 144 holds the short circuiting contacts 146 closed when the box is inactive, these contacts being connected to opposite sides of the line B. The lever-144 follows a wheel 148 which has a -stopping land 150. The wheels 130 and 148 are usually mounted on the same shaft. -The magnet 142 attracts an armature 152 which when the box is inactive is held depressed by the cam tooth 154 on the wheel 156 which is mounted directly in the rear of the code wheel 130. The 'code lever 136 and the armature 152 are mutually in- The wheels" are rotated by any tooth 154 moves off the armature 152. If the loo-x circuit is closed, the armature is held attracted by the magnet and the box is operative to transmit a signal by the opening and closing of the box circuit by the contacts 138 and 140 by the dropping of the code lever into successive teeth. However, if the box circuit is open at the time the armature is released, the armature moves into a position out of the effective field of the magnet, so that it will not be again attracted by the magnet during the remainder of the round, even though the box circuit may again be closed. This upward movement of the armature blocks the code lever, thereby preventing the box from sending in its signal and also holding the box circuit closed under contacts 138 and 140. If at any time during the sending in of a signal, the box circuit is open while the code lever is in its closed position, the armature will rise and prevent further operation of the box during the remainder of the round. At the termination of one round, the armature is mechanically depressed by the cam tooth and the box again feels of the line. If it finds the line open, it will be rendered inoperative for another round, but if it finds it closed, it will transmit its own signal. This type of box is non-interfering in that two boxes in the same circuit cannot possibly transmit a jumbled signal. It is also successive in that a box, after being pulled, will eventually transmit a signal even though it cannot gain control of the circuit immediately. Various modifications of this form of box are in common use, one particular type having provision for testing the line after four rounds, rather than at the'end of each round. All types of non-interfering and succession boxes operate on the same general principles and any one of them ma be successfully employed with the system of the present invention.

It will be understood that the invention is not limited to a'system employing only two box circuits. The number of box circuits may be increased indefinitely, it being only necessary to employ a. separate repeater for each circuit. The system commends itself because of its facility for expansion when additional box circuits may benecessary. A new repeater may easily be added to the system at any time by merely connecting its box circuit relay contact arms 29 and 38 into the wire 76, and connecting its non-interference magnet 44 across the lines L and L. 7

It will be seen that the system offers the advantages of simplicity of construction and reliability of operation. It is impossible to pull boxes so that they will in any way interfere. Complete protection is afforded against breaks in any part of the system. The parts of the system most susceptible to accidental opencircuits are the box circuits, but a fault in one of them renders only that circuitinoperative, the remainder standing ready to signal in normal manner.

Having thus described the invention, what is claimed is:

1. Arepea-ter having, in combination; a box circuit relay, a non-interference relay, interlocking armatures for the relays having provision for blocking one armature when. the other is moved from inactive position, a lower contact arm on the box circuit relay armature, an upper contact arm having provision for slight movement to permit closing of the circuitupon attraction of the armature prior to unblocking of the non-interference relay armature, and means for slowing'the movement of the contact arms after engagement thereof.

2. A repeater having, in combination, a box circuit relay, a non-interference-relay, interlocking armatures for the relays having provision for blocking. one armature when the other is moved from inactive position, a lower contact arm on the box circuit relay armature, an upper contact arm having provision for slight movement to permit closing of the circuit upon attraction of the armature prior to unblocking of the non-interference relay armature, and means for weighting the upper contactarm to retard the unblocking 'movement. 7 V 3. A repeater having, in combination, a box circuit relay, a non-interference relay, interloclzing armatures for the relays having provision for blocking one armature when the otheris moved from inactive position, and contacts associated with the armatures, one of the armatures having a hookto prevent unblocking thereof by the other armature when the latter is attracted, said hook being interposed in the path of movement of said other armature toward normal position.

t. A repeater having, in combination, a box circuit relay, a non-interference relay, interlocking armatures for the relays having'provision for blocking one armature when the other is moved'from inactive position, a lower contact arm associated with. the box circuit relay armature, an upper contact arm having provision for slight movement, the'contacts being adapted to close prior to unblocking of the non-interference relay armature, the box circuit relay armature having a hook whereby unbloclring thereof is prevented upon attraction of the. non-interference relay armature until the current builds up in the box circuit relay sufficiently to attractits armature, said hook being interposed in the path of move ment of said other armature toward normal position. I V

' 5. A fire alarm system having, in combination, box circuits, repeaters including a box circuit relay for each box. circuit,'con tacts controlled by the relays and adapted to be opened on the opening of an active box cuit associated with the time'relay contacts,

and means operated by the protective circuit for again closing the'inactive box circuits.

. 6.. A fire alarm system having,incombination, box circuits, a box circuit relay in each box circuit, a non-interference relay for each box circuit, the box circuit relayand non-interference relay having interlocking armatures whereby retraction of one armature blocks the other, non-interference lines connected with the non-interference relays to control the latter upon de-energization of any box circuit relay, the box circuit relay armature'having a contact, a movable contact arm associated therewith, a detent arm normally limiting the movement of the movable contact arm, a time relay connected with the non-interference lines and having contacts adapted to close upon opening of a box circuit longer than a predetermined time, tripping relays controlled by the timerelay having provision for attracting the detent arms to release the movable contact arms of the box circuit relays.

7 A fire alarm system having, in combination, box circuits, a repeater for each boxcircuit including a box circuit relay in v series with the box circuit and a non-interference relay, each relay having an. armature, the armatures of each repeater being interlocking whereby one armature when moved from inactive position blocks the other, a contact connected with the box circuit relay armature, a movable contact arm co-operating therewith, detent means normally holding the movable contact arm out of engagement with the armature contact when the armature is released, a repeater circuit including noninterference lines adapted to be energized through the contacts of the box circuit relays, a time relay having contactsadapted to close upon de-energization of the non-interference lines through opening of a box circuit for a predetermined time, tripping relays having armatures connected with the several detent means, and a circuitassociated with the tripping relays and controlled by the time relay contacts for releas ng the movable contact arm of the active box circuit relay to re-energize the non-interference lines. I

8. A repeater having, in combination, a box circuit relay, a non-interference relay, interlocking armatures for the relays having provision for blocking one armature when the other is moved from inactive position, a lower contact associated with the box circult relay armature, an upper contact arm normally engaging the lower contact when the box circuitrelay is energized, means for mounting the upper contact arm to permit pivotal movement thereof, a detent for normally limiting the movement, a tripping relay associated with the detent and adapted upon energization of the relay to release the upper contact arm whereby if the box circuit relay armature has been permitted to retract by a previous de-energization of the box circuit relay, the contacts may be again closed.

9. A fire alarm system having, in combination, normally closed box circuits, repeaters including a box circuit relay and a non-interference relay for each box circuit, a repeater circuit connecting the non-interference relays of each repeater, means controlled by de-energization of a box circuit relay to open the repeater circuit, means controlled by'deenergization of the repeater circuit to open inactive box circuits, a time relay connected with the repeater circuit and having contacts adapted to close upon de-energization' of the repeater circuit for a predetermined time due to a break in the active box circuit, a protective circuit associated with thetime relay contacts, means operated by the protective circuit for closing the repeater circuit and thereby to close the inactive box circuits, and means acting automatically upon repair of the break to recondition the repeater of the faulty box circuit for normal operation.

10. A repeater having, in combination, a box circuitrelay, a non-interference relay, interlocking armatures for the relays having provision for preventing retraction of one armature when the other is retracted, contacts associated with the box circuit relay armature for controlling energization 01 the non-interference relay including a lower contact arm and a movable upper contact arm adapted to engage with the lower contact arm, the lower contact arm having a hook interposed in-the path ofattracting movement of the non-interference relay armature to block the lower contact arm, and the upper contact arm having a'weight to retard move ment ofthe contact arms after engagement thereof with each other.

' 11. A repeater, having, 'in combination, a box circuit relay, a non-interference relay, interlocking armatures for the relays having provision for preventing retraction of one armature when the other is retracted, contacts associated with the box circuit relay armature for controlling energization of the non-interference relay including a lower contact arm and a movable upper contact arm adapted to engage with the lower contact arm, the lower contact arm having a hook interposed in the path of attracting movement of the box circuit relay armature to block the lower contact arm, the upper contact arm having a weight to retard movement of the contact arms after engagement thereof with each other, a detent for normal? ly limiting the movement of the upper contact arm, and a tripping relay associated with the detent to release the upper contact arm and permit it to fall into engagement with the lower contact arm. 8

12. A fire alarm system having, in combi nation, box circuits, repeater means for'each box circuit including a box circuit relay and a non-interference relay, armatures for the relays, interlocking means "for the armatures to prevent retraction of one armature when the other is retracted, contacts associated with each armature for controlling energizationfof the relayof the other armature and adapted to be closed during the first portion of the attractingmovement of a retracted Iarmature and prior to unblocking of the other armature, and means for delaying completion of the attracting movement of the armature after closure of the contacts.

, 13. A fire alarm system having, in combination, box circuits, repeater means for each box circuit including a box circuit relay and a non-interference relay for each box circuit, armatures for the relays constructed and arranged to be mutually interlocking, whereby, when one armature is retracted, the other is prevented from retracting, meanscontrolled y the box circuit relays to de-energize the non-interference relays, box circuit contacts controlled by each non-interference relay, means associated with the box circuit relay armature to temporarily prevent unblocking thereof upon retraction and subsequent attraction of the non-interference relay armature, and additional means associated with the box circuit relay armature to retard but not to prevent unblocking of the non-interference relay armature upon retraction and subsequent attraction of the box circuit relay armature.

14. A fire alarm system having, in combination, a plurality of normally closed box circuits, a repeater circuit having a plurality of repeater circuit contacts, one set for each box circuit, means operated upon opening of an active box circuit for operating its corresponding repeater circuit contacts fto abnormalize the repeater circuit, means acting upon abnormalization of the repeater circuit for opening inactive box circuits, and protective means operated after abnormalization of the repeater circuit for a predetermined time to normalize said repeater circuit contacts and thereby again to close the inactive box circuits.

'15. A fire alarm system having, in combination, a plurality of normally closed box circuits, a repeater for each box circuit including a box circuit relay and a non-interference relay, a repeater circuit connecting the non-interference relays, an armature for each box circuit relay, a movable contact arm carried by the armature, a second movable contact arm associated therewith, the contact arms having contacts in the repeater circuit, said contacts being opened upon retraction of a box circuit relay armature, and protective means acting to move said second contact arm into engagement With the first contact arm after opening of the repeater circuit for a predetermined time. p

In testimony whereof I have signed my name to this specification.

VERNON DUBBIN. 

